Which one of the following colours is not a part of the rainbow?  

The color that is not a part of the rainbow is: Grey
Important PointsThe colors of the rainbow, in order, are red, orange, yellow, green, blue, indigo, and violet (often remembered by the acronym ROYGBIV). Grey is not included in this spectrum.

• A rainbow is a meteorological phenomenon that is caused by reflection, refraction, and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky.
• This light takes the form of a multicoloured circular arc with the following colors in order: red, orange, yellow, green, blue, indigo, and violet. These colors are often remembered by the acronym ROYGBIV.
• Each color in a rainbow corresponds to a different wavelength of light. When sunlight enters a raindrop, the different wavelengths of light are refracted, or bent, at different angles — this is what causes the different colors to spread out into an arc.
• The color grey, however, is not part of the visible light spectrum. It is an achromatic color, a 'color without color', composed of a mixture of all frequencies of light in the visible spectrum.
• Because of this, grey does not appear in a rainbow, as a rainbow only includes colors that are found in the visible spectrum of light.